Recently, portable appliances such as notebook personal computers and cellular phones have become widely used, and there is thus an increasing demand for batteries as the power source for portable appliances. In particular, there is an increasing demand for secondary batteries that are small and light-weight, have high energy density, and can be repeatedly charged and discharged.
To meet such demand, non-aqueous electrolyte secondary batteries are under active research and development. Since non-aqueous electrolyte secondary batteries contain large energy due to an increase in the functionality of portable appliances, they generate large amounts of heat in the event of abnormal conditions.
Thus, proposals have been made on the structure of a battery pack containing such batteries, in order to suppress the conduction of abnormal heat, generated by a specific battery due to some reason, to adjacent batteries.
PTL 1 proposes disposing a partition plate with electrical and thermal insulating properties, made of a resin such as polypropylene or polycarbonate, between a plurality of batteries. The partition plate suppresses the conduction of heat of a specific battery generating abnormal heat to adjacent batteries.
In order to make the partition plate more flame-retardant, PTL 2 proposes using inorganic refractory materials such as mica and ceramics.
PTL 3 proposes forming a cavity in a partition plate made of an inflammable resin such as polyethylene or polypropylene and filling the cavity with a fire-extinguishing agent such as ammonium dihydrogen phosphate. In the event of abnormal heat generation of a battery, a part (a part with a low melting point) of the partition plate melts due to the heat, so that an opening is formed in the partition plate. The fire-extinguishing agent then flows out of the opening, and the empty cavity of the partition plate provides heat insulation.